STERNO WASTEWATER TREATMENT PLANT
SWEDEN
The objective of this study was to improve energy efficiency of a mid-size wastewater treatment plant by upgrading the aeration system and controls. One of two treatment lines at the plant were upgraded with a new blower, aeration grid and process controls while the other line was kept intact with existing equipment installed during the plant construction in 1997. The existing aeration system consisted of a lobe blower and tube diffusers and was controlled by DO control.
In the upgraded line, the aeration system consisted of a screw blower and Sanitaire Silver Series Low Pressure diffusers. It was controlled with a Sanitaire aeration control system consisting of cascade DO control, ammonia feedback control and most open valve logic. In addition, the DO profile was adjusted to the current load at the plant.
The two lines were operated in parallel from September 2011 to June 2012 and their operation was monitored with lab samples and online probes for evaluation of energy consumption and treatment performance. The 10 month long comparison showed a reduction in energy consumption in the upgraded line with 66% compared to the existing line. The airflow required was reduced with 35%. With these savings, the field aeration efficiency (measured as kg O2/kWh) was close to three times as high in the upgraded line as in the existing line. These large energy savings were a combined result of the more energy efficient blower as well as a higher oxygen transfer efficiency and lower pressure loss of the new aeration grid.
The Sanitaire process control system further decreased the energy consumption with a tighter and more accurate DO control, reduced pressure losses with the most open valve logic and a more efficient use of the aerated volume with the new DO profile. Improvements were also seen on the treatment performance with an on average 9% higher ammonia reduction in the upgraded line compared to the reference line. The largest difference was seen during the cold water period during which the nitrification was reduced at the plant. During this period, the ammonia reduction was 16% higher in the upgraded line.
